South Korea is radically different from the US. First, they are homogeneous. They all share the same culture. There are far less ethnic, social, and economic gaps in their society. Second, they are collectivist, and submission to the greater good is baked-in to the culture; way less of an independent streak than here. Third, they routinely wore face masks and practiced social distancing as a matter of course before this virus erupted; they remember SARS very well. Fourth, much, much smaller geographical footprint and the majority of the population concentrated in a few urban zones that can be closed off. Fifth, younger average population.
So the comparison is not good. We are more like a giant, more diverse Italy here.